Several studies have been conducted to look at whether Propecia works for hair loss in men. One study looked at using Propecia in men for male pattern baldness with hair loss at the very top of the head. At the beginning, the men who took Propecia grew new hair, while the men who took the placebo continued to lose hair. After about a year, the increase in new hair growth stopped for the men on Propecia, and these men started to slowly lose their hair again. However, the hair loss was much slower for the men taking Propecia than for the men who were taking the placebo.

After taking Propecia for five years, 48 percent of men had increased hair growth, 42 percent had no change (the hair loss had stopped), and 10 percent had lost hair. For the men who were taking the placebo, 75 percent had lost hair after five years. Also, once men stopped taking Propecia, the beneficial effects for hair loss wore off over one year.